Vehicular suspensions are well known for providing a smoother and more comfortable ride for driver and passengers. A typical embodiment for a rear suspension system utilizes a combination of leaf spring packs which provide support, and shock absorbers which provide damping; both of which are operatively attached between the axle and vehicular chassis frame. When traveling upon a rough road or off-road terrain, the vehicle wheels and axles can rapidly oscillate up and down; the frequency increasing with increased velocity of the vehicle and the severity of the terrain. This oscillation is facilitated by the vehicle's suspension system which determines the extent of vertical travel distance and degree of occupant comfort.
When a vehicle such as a pick-up truck has its cargo bed heavily loaded, the supporting springs compress downward upon the rear end causing the front end of the vehicle to rise. This downward movement of the frame towards the rear axle reduces the available vertical travel range of the rear suspension. For vehicles having their wheels positioned underneath the frame in a tire well, an extreme load could cause the tires to undesirably contact the vehicular body or cause the axle to contact the frame. As a preventative measure, rear bump-stops or limiters have been utilized such as those described in U.S. Pat. No. 5,857,687 issued to Ishii which while preventing damage to the vehicle, do little to address ride comfort of the occupants of the vehicle. The rear end sag also negatively impacts steering control and handling as the vehicular load is not properly distributed between front and rear suspensions.
Furthermore, pick-up truck manufacturers presently are designing trucks with the ride quality of a sedan in an effort to attract a broader customer base. To achieve this additional level of ride comfort, leaf spring-packs have been substantially lengthened. The drawback is that a longer spring-pack does not support as heavy a load as do shorter spring-packs. Also, longer spring-packs are susceptible to increased lateral twisting which increases the propensity for body roll. Many drivers do not carry substantial loads and these concerns do not become an issue. However, for vehicles which often carry heavy loads, longer spring-packs provide a comfortable ride when the heavy load is not present but cause the distance between frame and axle to become undesirably close when loaded. This reduced vertical distance is detrimental to ride quality. For this situation, the incorporation of a suspension enhancement becomes a necessity for improving ride comfort.
Prior art suspension enhancers are limited in their maximum displacement; i.e. from total compression to total stretch; otherwise known as wheel travel. A faster rate of wheel travel, i.e. a faster rate that the enhancer can change from total compression to total stretch, is highly desirable particularly in demanding conditions, such as off-road.
With respect to traveling in off-road conditions, it was observed that most vehicles are generally light weight and are unable to effectively stretch or elongate existing prior art suspension enhancers fast enough to keep both rear wheels fully in contact with the road surface. Ride comfort was further exacerbated when vehicles attempt to make sharp turns at higher speed the inside rear wheel will momentarily lose contact with the ground and traction is lost during this period.
One example of a prior art suspension enhancer is a product marketed by Timbren Industries Inc., Ajax, Ontario, Canada. The enhancer comprises an extended hollow cylindrical-shaped piece of resilient rubber which replaces the factory bump-stop and is attached to the vehicular chassis frame. The product when installed, does not contact with the adjacent axle; rather, it provides a spacing such as 1 inch or more. When the bed of a pick-up equipped with this product is loaded with sufficient weight, the vehicle frame will lower and the product will contact the vehicle axle. While this product does provide additional support and ride comfort when an increased load is being hauled, the product is detrimental to ride comfort in situations where no additional load is being hauled. For this lighter-load situation, the product will only contact the adjacent axle when the axle displaces upward as a result of a compression event occurring; such as when the vehicle traverses a speed-bump, pothole or other roadway elevation. This contact is more aptly described as an impact event since the rubber contact with the axle is often hard and sudden, and a suitable damping effect is lacking as undesired oscillation can continue for some time.